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The only place where afterCreateChannel callback is added is 
https://github.com/RocketChat/Rocket.Chat/blob/develop/packages/rocketchat-piwik/client/trackEvents.js#L29
where the callback has the created room as the only argument.

My server logs were being spammed with gravatar fetch errors. I don't think it's worth reporting as an error when gravatar service returns a 404, it just means that email doesn't have a gravatar associated, which is pretty common.